Historically, complete removal of a disc from between adjacent vertebrae resulted in fusing the adjacent vertebrae together. This “spinal fusion” procedure, which is still in use today, is a widely accepted surgical treatment for symptomatic lumbar and cervical degenerative disc disease. More recently, disc arthoplasty has been utilized to insert an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae. Such implants have been inserted into lumbar, thoracic, and cervical intervertebral spaces between adjacent vertebral bodies through an anterior, antero-lateral (oblique), lateral, extraforaminal, transforaminal, or posterior surgical approach.
Such disc implants can provide for limited universal movement of the adjacent vertebrae with respect to each other. The aim of total disc replacement is to remove pain generation (caused by a degenerated disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. As a result, the trunk, legs, and pelvis are in equilibrium and can maintain harmonious sagittal curves and thus promote the damping effect of the spine.
One such intervertebral implant includes an upper part mounted to an adjacent vertebra, a lower part mounted to another adjacent vertebra, and a cavity located between the upper and lower parts. The cavity can be intraoperatively filled with organic, such as allograft, and/or synthetic, such as beta-tricalcium phosphate, bone graft substitutes to promote fusion between the implant and adjacent vertebra. More recently, the cavities of such implants have been pre-filled with a synthetic bone graft substitute prior to implantation into the intervertebral space. Such implants are often made from a metal, such as titanium, or polymer. During the implantation procedure, the vertebral bodies are distracted so as to expand the intervertebral space to a height that allows clearance for the insertion of the implant. Once the implant has been inserted, the distraction forces are released, thereby allowing the vertebral bodies to return to their resting position against the implant.